Method of making tennis balls



Sept. 25, 1928. 1,685,423

. L. R.'HURLBURT METHOD OF MAKING TENNIS BALLS Filed Nov. 1927 INVENTOR ahhmaw Patented set. 25, 1928.

UNITED STATESVPATENT' OFFICE;

LEE 3. HUBLBURT,OI JEANNETTE, PENNSYLVANIA, ASSIGNQR TO PENNSYLVANIA RUBBER COMPANY, 01 JEANNETTE, PENNSYLVANIA, A CORPORATION 01' PENN- srnvama Application filed November 8, 1927.

My'invention relates to the manufacture of hollow rubber spheres, and findspractical application in the manufacture of tennis balls.

manufacture .the hemispherical shells. are.

molded and semi-cured; the semi-cured shells are brought together edge to edge and in- ,tegration across the seam as well as vulcanization are effected while the body of rubber is under compressive strain. This ordinarily is efiected within a: snug-fitting mold, and,

operating with such strain as the mold itself may exert, the body of, air or other gas within --the ball will under the heat of vulcanization,

tend to expand, and so to act compressively upon the rubber. The. meeting edges of the hemispheres are ordinarily beveled, with the ends in view of increasing theareasof adhesion and of obtaining a smooth seamex ternally, at least. -But while the seam may be smooth on the outside, there is apt to be displacement within, and the development along the seam of an inwardl extendmg fin of rubber. This is undesirab e .both becauseit-is a waste of rubber and because the result is an unequal distribution of the whole mass not" only is there no' displacement of edge upon- 01f1 rubbpr an -a con uent failure to' attain t e per ect symmet y I have discover d l rubber and this development of an interior fin to be due to the comprmve strains towhich.

- I have alluded acting upon the thin and plastic walls. And my invention consists in such a modification in the shape of the meeting edges that displacement is guarded against and prevented. I form the edges of the hemi' spheres with complementarytongue and groove, 'andwhen the hemispheres are united and when in the mold the body ofrubber is heated andsubjected to compressive strain,

edge, but alignment is accurately maintained, the compressive strains are wholly effective toward the intended end, and the result is a better balanced and more efiectively integrated ball. x n

. My myention is illustrated in the accompanying drawings. I is a fragmentary this; displacement of' ma'rnon' or name 'rmmrs rants.

Serial No. 231,957. 7 n I view in section on a plane-perpendicular to the seam showing, in adjacent positions the edges of two hemis heres, which will be understood to be hemispheres of soft rubber, about to be united in the making of a tennis ball. Fig. II is a like view, illustrating a modification. Fig. III is-a view to larger scale, illustrating a minor modification of the shape of the article as seenin Fig. II.

The hemispheres are molded, after I the manner known-to the art,and pre ared for union one with another in what is ca led semicured or semi-vulcanized condition.

In the practice of my invention I shape the edges, not to the usual square or beveled abutting surfaces, but to companion tongue and groove. Preferably the tongue and groove are-shaped on simple and approxi-. mately semi-circular curves, as shown in Fig. I. They may be sha d to projecting and reentrant angles, as s own in Flg. II; .and in either case the complementary edges may be so particularly shaped as to leave at the bottom. of. the groove when the edges have been brou ht'together, a narrow ace for the a'ccumuIation of any} su lus o cement. Such provision appears int etruncating of the projecting angle, illustrated in F1.III.tin -"d-.* e mee g are cemen er and the cement m a y be of one sort gi- 811- other, but in any case it will at the time of ap lication be morefluid than the rul iber tothe of which it is ap lied. Pr'ferabl I emplo rubber cement, at is to say ru ber disso ed in a relatively volatile solvent. The rubber which is em loyed may be substantially the rubber mix of which the hemispheres themselves are formed. When the cement has been applied and the hemispheres united, the solvent is dispelled,

and a practically homogeneous seam is formed. If the cement be of a softer and permanentl more lastic substance than the rubber oft 'e finis ed ball, then the ball in play will stretch at the seam more than else-- where; conversel if the cement be relatively be placed-in the two alves of the vulcanizhard, the stretchin a the seam will be less.

ing mold and, the edges being properly pre- I pared, the halves may -be brofiht together on the closing of the mold. te rnatively,

the hemispheres pro erly supported ma initially be stuck toget er, and then intro uced into the mold. In one case the seam will lie in the meeting plane of the mold halves; in 5 the other case the position of the seam of the ball Within the mold will be accidental and will vary indefinitely.

The ton ue-and-groove connection may be minutely shaped as preferred. I have shown in Fig. I the preferred approximately semicircular shape, in Fig. II a V-shape, and in Fig. III, V-shape with truncated apex. Manifestly the showing does not exhaust the known forms of tohgue-and-groove joints.

I have spoken of the ball parts as hemispheres and of the seam as being equatorial. This is substantially true. The position of the seam may, however, vary somewhat from an accurately equatorial position.

It is because a tennis ball is thin-walled and formed of relativel soft rubber that the difficulties of manu acture to which I have addressed myself exist. Thewall is actually in thickness about one tenth of the 25 radius of the sphere. I

I have said nothing about inflation and be inflated.

inflation means. Tennis balls contain air or equivalent gas under pressure somewhatexceeding atmospheric. This excess pressure may be achieved by chemical reaction within the closed chamber of the ball, or by manufacture in a chamber where the desired excess pressure is maintained, or by penetration of the wall of the ball by an inflating needle, with provision that upon withdrawal of the needle, the puncture will automatically close. My invention may be practiced in the manufacture of the ball, by Whatever means it may I claim as my invention:

As a. step in the manufacture ofhollow rubber spheres the method herein described which consists in preforming two hemispherical shells of semi-cured and relatively plastic. rubber with edges shaped to complementary tongue and groove, and vulcanizing into an integral sphere of elastic but nonplastic material, the shells while held under pressure to edge-to-edge engagement.

Intestimony whereof I have hereunto set 50 my hand.

LEE R. HURLBURT. 

